Volatile metal-.beta.-diketonate and metal-.beta.-ketoiminato complexes are used in a wide range of applications including trace metal analysis by gas chromatography, studies of the stereochemistry and isomerization of metal complexes, ligand exchange, gasoline antiknock additives and in the vapor deposition of metals.
Metal .beta.-diketonate complexes used as metal precursors in chemical vapor deposition processes must be of high purity and guaranteed volatility. The demand for high purity and guaranteed volatility is particularly acute in the electronics industry. Metal-ligand complexes are typically sold in the form of the hydrated or solvated adduct. While some specialty chemical manufacturers offer anhydrous metal-.beta.-ketonate complexes, these complexes are typically prepared by utilizing a non-aqueous solvent such as methanol wherein the complex is sold in the form of a solvated adduct (i.e., M(L).sub.2.MeOH). These adduct complexes often do not satisfy the stringent requirements imposed by some sensitive processes and are difficult to isolate requiring cumbersome purification schemes involving recrystallization.
Attempts have been made to effect the liquid-phase condensation of a primary amine or a primary diamine with a ligand represented by Formula I: ##STR1##
In substances in which R.sub.1 and R.sub.2 are not both fluorocarbon groups, the literature reports that one of the ketone oxygens can be replaced with a nitrogen atom from an amine group by direct Schiff-base liquid-phase condensation between an appropriate .beta.-diketone and an amine. Additionally, the corresponding metal complex can be synthesized by chelation to a metal species. See A. E. Martell, et al., J. Inorg. Chem., Volume 5, pp. 170-81 (1958).
As reported by Sievers, et al., in J. Inorg. Nucl. Chem., Volume 32, pp. 1895-906 (1970), ligands according to Formula I wherein both R.sub.1 and R.sub.2 are perfluoroalkyl and in which an oxygen atom has been replaced with an amine to form a ketoimine, have not been obtainable utilizing liquid-phase or vapor-phase conditions.
A need exists in the art for a process capable of preparing highly volatile metal-ligand complexes in high purity wherein the ligand is a .beta.-diketone or .beta.-ketoimine, each of which may also be partially or fully fluorinated. Unfortunately, typical liquid phase processes for preparing such metal-ligand complexes have fallen short of providing the broad range of structures and level of purity required in many current applications such as those employed in the electronics industry.